Monocytes are being characterized for the expression levels of CD40, CD80, CD86, CD120b, and the gamma interferon receptor alpha chain. These studies have identified 2 patients with gamma interferon receptor alpha chain deficiency, and the molecular level of this defect is being actively examined. There are emerging data that CD120b expression may also be abnormal in some patients with recurrent mycobacterial infection. Specific expression of the gamma interferon receptor alpha chain is being evaluated on amniocytes as a possible approach to prenatal diagnosis of this disorder.